The disclosure generally relates to inductor devices and, more particularly, to embedded inductor structures with an improved quality factor.
Inductors have been widely used in circuits such as resonators, filters, and impedance transformers. Conventional inductors are mounted on circuit boards utilizing the surface mounting technique (SMT) or other complicated processes, and they may occupy an undesirably large area or exhibit an undesirable height on the circuit boards. To reduce the size, embedded inductors have been developed. FIG. 1A and FIG. 1B are diagrams of an embedded spiral-type inductor in the prior art. FIG. 1A is a top plan view of a spiral-type inductor 10 in the prior art. Referring to FIG. 1A, the spiral-type inductor 10 is formed on a multilayered substrate 11 and includes a conductive coil 13 extending from a port 1A to a port 2A through a conductive path 14 formed in a different layer of the multilayered substrate 11. FIG. 1B is a cross-sectional view of the spiral-type inductor 10 along a line A1 shown in FIG. 1A. As illustrated in FIG. 1B, the conductive coil 13 of the spiral-type inductor 10 is formed on a layer 111 of the multilayered substrate 11, and the conductive path 14 is formed on a layer 112, which is electrically connected to the layer 111 through conductive vial V11 and V12.
The quality factor (Q-factor) of an inductor incorporated into a communication system may largely determine the communication quality. For example, an inductor with a low Q-factor may incur significant insertion loss in the pass band of a filter and may increase the bandwidth of the filter, which renders the system more liable to noise. As another example, an inductor with a low Q-factor may incur undesirable phase noise in a resonator, which may deteriorate the quality of a communication system.
Many inductor structures have been proposed to provide an improved Q-factor. Examples of the inductor structures can be found in the prior art techniques as follows. U.S. Pat. No. 5,373,112 to Kamimura, entitled “Multilayered wiring board having printed inductor,” disclosed a multilayered wiring board having a printed inductor which is formed on a grounding layer or electric power supply layer through a dielectric layer inserted between them, wherein a removed portion is formed only in the grounding layer or electric power supply layer which is positioned right under the printed inductor and in the neighboring area and no removed portion is formed in the dielectric layer. U.S. Pat. No. 6,175,727 to Mostov and Letzion, entitled “Suspended printed inductor and LC-type filter constructed therefrom,”, and U.S. Pat. No. 6,448,873 to Mostov and Letzion, entitled “LC filter with suspended printed inductor and compensating interdigital capacitor,” introduced suspended-structured printed inductors in order to increase the Q-factor of an inductor. U.S. Pat. No. 6,800,936 to Kosemura et al., entitled “High frequency module device,” disclosed a device where metal conductive portions under an inductor formed on a built-up multilayered substrate are removed by etching to reduce parasitic effect in order to increase the Q-factor of the inductor. However, the above-mentioned prior art structured or processes may be complicated in certain applications. Therefore, there is a need for an inductor that has an improved Q-factor under certain configurations and a structure that is easy to fabricate with semiconductor processing or PCB processing.